Accurate localization of electrical sources in the brain using EEG's or MEG's measured on the surface of the head has important clinical and research applications. Localization is most simply and easily done by calculating inverse solutions in a spherical model of the head. However, modeling errors caused by the differences between the geometry of actual heads and a spherical model produce localization errors. Studies performed in previous periods of this grant and by others have investigated the effects of various "regular" or symmetrical modeling errors on localization accuracy. Adequate studies of the effects of combinations of modeling errors and/or actual "irregular" head geometry on localization accuracy have not been performed. It is proposed to perform such studies using realistic computer models of the head developed from X-ray, MRI, CAT, anatomical model, and/or physical measurement data. EEG's and MEG's produced by sources in these realistic models would be calculated. These EEG's and MEG's would then be used to calculate inverse solutions in a spherical model. The effects of realistic head geometry on localization accuracy would be determined by comparing the inverse solutions with the source locations in the realistic models. As part of these studies, methods of fitting a spherical model to actual heads will be investigated to determine which method produces the greatest localization accuracy. Similarly, investigations of measurement grid parameters, such as density of measurement points, size of grid, etc., will be performed to determine which parameters produce the greatest localization accuracy. The results of these investigations will provide methods for the most accurate source localization using a spherical head model. This will provide a simple, inexpensive method for source localization which can be easily and widely used.